In the recent drive for higher integration and operating speeds in LSI devices, the pattern rule is made drastically finer. The background supporting such a rapid advance is a reduced wavelength of the light source for exposure. As the light source wavelength has been shortened from i-line (365 nm) of a mercury lamp to KrF excimer laser (248 nm) and further to ArF excimer laser (193 nm), the fabrication of 65-nm node devices is under practical investigation. Additionally, a study is started on the ArF immersion lithography wherein ArF excimer laser is irradiated through water held between the projection lens and the wafer. A combination of a lens having NA of at least 1.2 with ultra-high resolution technology suggests a way to the 45-nm node and forward (see Proc. SPIE Vol. 5040, p 724, 2003).
The ArF immersion lithography has a possibility that water-soluble components in the resist film be leached in immersion water during exposure. Specifically an acid generated during exposure and a basic compound previously added to the resist material can be leached in immersion water. As a result, pattern profile changes and pattern collapse can occur. It is also pointed out that water droplets remaining on the resist film after scanning, though in a minute volume, can penetrate into the resist film to generate defects. It was then proposed to provide a protective coating between the resist film and water to prevent resist components from being leached out and water from penetrating into the resist film, which process is known as topcoat process (see 2nd Immersion Workshop: Resist and Cover Material Investigation for Immersion Lithography, 2003).
In the ArF immersion lithography using a topcoat, a protective coating material which is soluble in alkaline developer is advantageous. This eliminates the step of stripping off the protective coating, offering great cost and process merits. Thus, great efforts have been devoted to develop water-insoluble resist protective coating materials, for example, resins having alkali-soluble units such as fluorinated alcohol, carboxyl or sulfo groups. See WO 2005/42453.
On the other hand, a process for preventing resist components from being leached out and water from penetrating into the resist film without a need for a protective coating material has also been developed, the process being referred to as “topcoatless process”. See JP-A 2006-48029 and JP-A 2006-309245. In the topcoatless process, an alkali-soluble hydrophobic polymer is added to the resist material, whereupon the hydrophobic compound is segregated at the resist surface during resist film formation. The process is thus expected to achieve equivalent effects to the topcoat process, and is more cost effective because steps of forming and removing the protective film are unnecessary.
In either of the topcoat and topcoatless processes, the ArF immersion lithography requires a scanning speed of about 300 to 700 mm/sec in order to gain higher throughputs. In the event of such high-speed scanning, if the water repellency of the resist or protective film is insufficient, water droplets may be left on the film surface after scanning. Residual droplets may cause defects. To eliminate such defects, it is necessary to improve the water repellency of the relevant coating film and the flow or mobility of water, i.e., water slip (expressed in terms of receding contact angle) on the film.
One exemplary material known to have excellent water repellency and water slip on film surface is a copolymer of α-trifluoromethylacrylate and norbornene derivative (Proc. SPIE Vol. 4690, p 18, 2002). Another example of the highly water repellent/water slippery material is a fluorinated ring-closing polymerization polymer having hexafluoroalcohol groups on side chains. This polymer is further improved in water slip by protecting hydroxyl groups on side chains with acid labile groups, as reported in Proc. SPIE Vol. 6519, p 651905 (2007).
Although the introduction of fluorine into a polymer structure is effective for improving water repellency and water slip, the introduction of extra fluorine can induce new defects known as “blob defects”. Blob defects are likely to form during spin drying after development, particularly when the film has a high surface contact angle after development. One approach for suppressing blob defects is by introducing highly hydrophilic substituent groups (e.g., carboxyl or sulfo groups) into a resin to reduce the surface contact angle after development. However, since these groups serve to reduce the water repellency and water slip of the resin, this approach is not applicable to high-speed scanning. There is a desire to have a resin material which can minimize blob defects while maintaining highly water repellent and water slip properties during immersion lithography.
The highly water repellent/water slippery materials discussed above are expected to be applied not only to the ArF immersion lithography, but also to the resist material for mask blanks. Resist materials for mask blanks are subject to long-term exposure in vacuum. It is pointed out that sensitivity variations or profile changes can occur as an amine component in the resist material is adsorbed to the resist film surface during the long-term exposure. It was then proposed to add a compound having surface active effect to modify the surface of a resist film for preventing adsorption of amine to the resist film.